Laser printers and/or digital printing presses, for example dry toner laser printers and liquid electrophotographic (LEP) laser printers, to name a few, generally use a discharge area development (DAD) electrophotographic process in which light is used to selectively discharge electrical charge on a photoconductor to form a latent electrostatic image. Electrically charged toner or ink is then applied to the photoconductor and adheres to the photoconductor in either exposed or unexposed regions in which the electrical charge has been discharged but does not adhere to the unexposed or exposed regions, respectively, which have not been discharged. The adhered toner or ink is then transferred to a print medium such as paper and bonded onto the print medium.
Errors in the scan lines produced on the photoconductor can produce visible artifacts in the printed image on the print medium, which are undesirable. These errors may be caused, for example, by non-uniform exposure energy density for a particular region of photoconductor. The exposure density can be regarded as the product of the power density (normally measured in mW/cm2) of the light incident on the photoconductor and the exposure time of the photoconductor by the light for that region of the photoconductor.
Thermal cross talk can negatively affect the power performance of lasers. Thermal cross talk can be illustrated by an example. When a certain laser remains in a “switched on” condition, while one or more surrounding lasers are switched from an “off” to an “on” condition (or vice-a-versa), the temperature of the die of the first laser can increase (or decrease) due to the dissipated heat of the surrounding lasers. This rise in temperature can cause a power decrease of the first laser. In general, changing temperature conditions of neighboring lasers, for example due to modulation, may cause undesired heat exchanges between the lasers, and in turn affect light intensities.
The effect of thermal cross talk is seen as an intrinsic characteristic of laser arrays. Thermal cross talk can become worse in laser arrays of relatively short wavelength, for example red lasers, for example under 700 nanometers. In infrared laser arrays of approximately 830 nanometers, light intensity is usually affected less than 10 percent, while for red lasers having wavelengths between approximately 630 and 670 nanometers, the intensity can be affected more than ten or even several tens of percent. In one explanation, due to the relatively low thermal conductivity, higher electrical resistance and higher voltage threshold of these types of lasers, more heat is dissipated in the laser die.
It may therefore be desired to limit thermal cross talk in laser arrays, and in laser arrays for electrophotographic printing.